A black-tailed sea hare—just one of the more than 100 species of sea slug that glide through our waters—grazes on the seaweeds that make up its diet. Handsome they may be, but sea slugs have a lot more going for them than just good looks.

Magazine

Jan - Feb 2005

New Zealand Geographic readers may recall from 1999 and 2002 issues of this magazine, the walk stories from Te Araroa—The Long Path. A lone hiker—it happened to be me—just went out and did it, Cape Reinga to Bluff.
But the trail at that point, though designed to incorporate as many existing walking routes as possible, was still, as one journalist friend liked to point out, “notional.” That 2,920 km walk was the best of times, and occasionally the worst of times: darkness in trackless country, dense cloud on the tops, uncertainty at the fork in the path, ice and snow, fear of rivers, and once—reverting here to a Grimm brothers archetype—the eyes of a wild creature glinting out from a lonely hut.
The worst of times are, as every tramper knows, great fun really and in retrospect a doddle compared to the still more profound “fun” of the next stage—actually putting the trail in.
Te Araroa Trust always intended translating the notional trail into a real one. The result: long and sometimes painful negotiation with landowners, the continual scrabble for funding, but also steadily advanc­ing success.
It’s five years since we got our first big millennium grant, and began our first track construction in the Waikato. The progress over those years has always been steady. The Mayors’ Taskforce for Jobs gave us a lift in 2002 when it adopted the idea, the Department of Conserva­tion also when it signed a Memoran­dum of Understanding agreeing to assist the mutual goal as Te Araroa’s route crossed over DoC estate. And out of left field came the whisper from Maori in the north, passed on by Shane Jones after we put a 15 km trail across the Herekino Forest, that the old people had begun to talk of the trail as te ara tawhiti, te ara roa,te ara hou. The path of distance, the long path, the path of spiritual renewal.
We opened three new north-south trails in the years 2001–2003, aligned where possible to existing tracks, or to accessible coastline so as to advance a continuous route. Sir Edmund Hillary, a great sup­porter, was always there for the opening hoopla. Important too was council participation. One council, Whangarei District, adopted respon­sibility for the whole Te Araroa route through its territory. Other councils like Waikato District were writing it into their district plan, or, like Rod­ney and Wellington, setting money aside for development. Environment Waikato weighed in as a supporter, and the Maori Queen Dame Te Atairangikahu, lent her personal support for the Waikato river leg, now extending over 30 km and counting.
But it was in 2004 that the trail took its great leap forward. Last August, Canadian country-pop star Shania Twain and husband Robert ‘Mutt” Lange guaranteed Te Araroa access through their newly pur­chased domain between Wanaka and Queenstown. That concession—and a strip around Lake Wanaka’s shore­line obtained during Crown Tenure Review—made possible a 48 km route between Wanaka and Arrow-town, with the trail still to be unrolled there, but with most of the budget guaranteed by Shania and Mutt.
And let’s not forget the metropo­lis, for the trail differs from the tra­ditional New Zealand back-country tracks. It deliberately links settle­ments, towns and ten cities.
Through the efforts of Te Araroa worker Miriam Beatson and North Shore City, a 23 km urban trail was signed through the city. On No­vember 21 this year, Allison Roe, a former world record holder for the marathon, opened the track and led the first ceremonial walk. Auckland City had already agreed to piggyback Te Araroa on its Coast to Coast trail, and Manukau City has now written the route into its walkway plans.
In that same astonishing Novem­ber week the Christchurch company City Care put a 12-person gang to work under its operations manager and trail enthusiast Brian Keown. The team had three trucks, a hi-ab, and a digger, and in just five days added another 58 km to Te Araroa. This Tekapo to Twizel section is now open to both hikers and bikes. Meantime, Te Araroa construction manager Noel Sandford and a small gang have also been working at speed this year to complete link­ing trails through the countryside between Hamilton and the Pirongia summit, down from there through the countryside to Waitomo, and up the Mangaokewa River south-east of Te Kuiti. All of it adds up to 250 km of trail either built or corridor-secured along the proposed north-south route. The actual distance achieved is much greater. Since the new trails link to existing public ac­cess, we now figure we’ve achieved continuous walking routes for over half Te Araroa’s total—most of it off-road, and with the rider that most of that is not yet specifically signposted.
But ever onward: the Department of Conservation undertook its Recre­ation Opportunities Review this year, inviting submissions from the public, and it became apparent the depart­ment was giving the new trail serious support. The Red Hills hut north of St Arnaud had been trashed for years and was marked down for demoli­tion in the review. Following Te Araroa Trust submissions, it’ll be re­built on an alternative site, allowing a one-day walk down to St Arnaud. In the Canterbury Conservancy, the swing bridge across the Otehake River was scheduled for removal. The river is a major hazard after rain, and it’s on Te Araroa’s route. Follow­ing our submission, among others, the swing bridge will now stay. In the Waikato Conservancy, a new hut is under construction to serve both a loop track in the Hauhungaroa Range, and provide a stopover on the direct Te Araroa route.
There was uncanny serendipity too with land purchases in the South Island. Both the 4,000 ha of Pop­lars Station, bought last August by the Nature Heritage Fund for $1.89 million, then Birchwood Station on the upper Ahuriri Valley, had distinct conservation values. But both hap­pened also to be on Te Araroa’s proposed route east of the Alps.
The long path project also now has six regional trusts—Auckland, Waikato, Manawatu, Wellington, Canterbury and Otago, with South­land soon to sign up. The new trusts bring a power of skilled and largely volunteer effort to bear on scop­ing Te Araroa, knitting in the DoC conservancies, the regional, district and city councils, and where neces­sary, funding construction. They have access to a digital atlas refined by Te Araroa trustee Kim Ollivier so that land ownership and terrain can be traced at 1:5,000 detail. As Te Araroa Trust and its regional arms establish the route, that atlas will be opened to the public via Te Araroa’s website and the walking of New Zealand can begin. The finish date for the track is 2008. It’s an optimistic date, but if the unrolling continues at 2004’s rate it’ll be the year to celebrate a trail I predict will become world famous, and not just in New Zealand.

Although numerous museums have disabused me of the notion that spe­cial collections have to be displayed in stodgy, poorly lit, indoor spaces, the idea of an open-air native plant museum like Otari–Wilton’s Bush, in Wellington, still intrigues me. But, when one considers that the root of the word “museum” comes from the Greek mouseios, meaning “of the muses”, an outdoor museum dedi­cated to native plants seems more comprehensible. In fact, in Greek mythology, the nine sister muses preside over song, poetry, arts and sciences, and on any given weekend visitors to Otari–Wilton’s Bush might indulge in one or more of these pursuits.
About 1200 plant species are rep­resented in the reserve, which is the only botanic garden devoted solely to New Zealand’s native plants. It features more than 100 ha of native forest and 5 ha of native plant col­lections, and for much of its life has been known as the Otari Open-Air Native Plant Museum.
The plants to which it is home come from all over New Zealand, including from the Kermadec Islands, 1000 km north-east of Auckland, and from Campbell Island, some 700 km south of Bluff. Botanists, plant taxonomists, cytologists, ethnobota­nists and garden enthusiasts come from all over the world specifically to see the collections. The reserve averages 95,000 visitors a year.
Like any museum, Otari–Wilton’s Bush features some special collec­tions that attract aficionados from near and far. Whereas your conven­tional museum or art gallery might be known for its old Maori carvings or Rita Angus paintings, here there are assemblages of flax cultivars, hebes, grasses, pittosporums, coni­fers and more.
Other visitors are drawn to Otari–Wilton’s Bush by the op­portunity to see some of the rarities to be found there. For instance, Coprosoma acerosa, now extinct in the wild, formerly grew only near the Red Rocks of Wellington’s south coast, where it was wiped out by pest animals that foraged on it and non-native weeds that displaced it. Fortunately, there are places such as the reserve where it is now not only cultivated but thriving. It is difficult to view this woody, milk-chocolate­coloured, low-growing plant without feeling a sense of awe.
Some of the plants brought to the reserve from the Three Kings Islands, 60 km north-west of Cape Reinga, are represented in the wild by only single specimens. Several are now grown in gardens, including Pen­nantia baylisiana, a lush-looking tree with big glossy leaves, and Tecoman­the speciosa, a vigorous vine with white trumpet-shaped flowers. Both can be viewed in the reserve’s wild garden.“Every plant here has a story,” says Robyn Smith, the reserve’s cura­tor, as she takes me on a tour. She tells me about a small geranium with the tag name (what a plant is called before it is formally identified and named) Geranium aff. sessiliflorum (“Von River”). “It’s quite hard to see because it’s so small and well dis­guised. Its grey-green leaves have a funny red splotch on them, and each leaf is only about 1 cm wide. The plant was unintentionally discovered beside the Von River in Southland by the late Tony Druce, a botanist. I say unintentionally because he brought back a chunk of soil with some plants on it and potted it. Only then did this lovely little geranium pop up; he had no idea it was in the soil when he brought it home. No other specimen has ever been located in the wild, but the reserve now cultivates it. And, as every gardener knows, geraniums can grow like weeds, so it’s done quite well here. We’ve sent plants down to DoC Otago so they can study and learn about the plant’s attributes first­hand. Reserve plants frequently help fill information gaps.
“It makes me crazy when people say that New Zealand plants are bor­ing,” Smith continues. “Just because they’re not garish doesn’t mean that they’re not interesting. New Zealand plants have form, texture and subtle beauty.”
Her words would have warmed the heart of Dr Leonard Cockayne, the renowned botanist and first director of the reserve in the days when it was called Otari Open-Air Native Plant Museum. In numerous books and papers, Cockayne wrote ardently about the many distinctive plants found in New Zealand. In his seminal work, New Zealand Plants and Their Story, published in 1910, he declared: “There are thousands of acres fit only for the natural growths now clothing them, and the destruc­tion of these forests would be a fatal mistake.” Such sentiments explain why he worked so diligently in the 1920s with J.G. MacKenzie, director of Wellington Parks and Reserves, to devise a plan for a local open-air plant museum.
Before European colonisation, the Wilton area was densely forested with rimu, northern rata and tawa. The forest provided a prime hunting spot for local Maori, who called it Otari, or “place of snares”.
From the mid-1800s to the early 1900s, the area fell under the owner­ship of various settlers. One of these, Job Wilton, farmed much of the land but protected a sizable forest around his home, some of which now stands
Then, at the turn of the century, peo­ple looked around and realised what they had lost, and they scrambled to save this last teeny, tiny remnant of forest. We owe a great debt to the likes of Job Wilton and some of the residents of Wellington who were willing to preserve the area until the government could afford to acquire it in 1906.”
In 1918, the land was transferred to the city of Wellington for “recrea­tion purposes and for the preserva­tion of native flora”. As a result of the vision of MacKenzie and Cockayne, in 1926 the site became the Otari Open-Air Native Plant Museum. The objectives of the reserve haven’t changed much since that time. The original four-point scheme still holds: to establish a collection of as many New Zealand species as possible for cultivation in the museum; to propagate various important types of primitive vegetation typical of New Zealand; to restore the bush area to its original form; and to illustrate how indigenous plants could be used in home gardens and for other horticultural purposes.
Although the reserve has re­mained steadfast over the years in pursuit of these goals, its name has varied. Under curator Walter Brock­ie, it was changed to Otari Gardens in 1949, only to revert to the former designation after Brockie’s tenure came to an end. In 2000 it became Otari–Wilton’s Bush in recognition of both Maori and European influ­ence as well as the significance of the native bush that remains.
The reserve’s impressive plant collections rightfully receive a lot of attention, but the native bush too, is a joy to tramp through—there are 11 km of tracks—and it is important both for wildlife and for the insight it provides into original and regenerating podo­carp forest. Rimu, kahikatea, totara, miro and matai all flourish. Kawakawa and various climbing plants, ferns and epiphytes also abound.
“The birds have come back to the forest over the past few years,” says Dave Bidgood, a collection curator who has worked at the reserve since 1994. “A visitor used to be lucky to see a fantail or two in the re­serve. Now we go out in the morning and see nine tuis on a single tree. Last spring we even had a confirmed sighting of a robin on one of our tracks here. The num­bers of kereru, tomtit and other birds started increasing once we got serious about pest control in 1993. It’s kind of exciting to realise that our native plants here are again providing habitat for native birds.”
Revegetation work by volunteers and a part-time staff member over the past five years along part of the Kaiwharawhara Stream both inside and outside the reserve has also enhanced the area’s value to wildlife.
As I walk along with Smith, we wander by the fern­ery, which is one of my favourite parts of the reserve. I mention this to her and she tells me that the storms in August 2004 felled a large tree nearby and that the ex­tra light getting in is adversely affecting some ferns. As Cockayne wrote, “Though many plants are eager to get into the fresh air and sunlight, others are the reverse, and have developed different adaptations in accord with other aspirations.”
Smith helps me grasp just how much effort goes into protecting and maintaining a living museum. With many plants in the collections classified as rare or endangered, and overseeing one of Wellington’s few regenerating native forests a heavy responsibility, the stakes are high.
Otari–Wilton’s Bush may indeed have been inspired by the muses, but its preservation is due to those who have been willing to get dirt under their fingernails and calluses on their hands, and to share our native flora’s.

On October 25, 2004, the New Zealand Herald ran a cover story un­der the headline “DoC losing battle to save rarest species”, proclaiming that the New Zealand Department of Conservation (DoC) was simply unable to protect all threatened spe­cies, and that consequently many might become extinct or key popula­tions die out. The main species to feature were animals, such as the kakapo, kiwi, Hookers sea lion and katipo. One mysterious Canterbury plant was also mentioned but no name was given. While it cannot be denied that these organisms occur in much lower numbers than in the past, and some do indeed face pos­sible extinction, their parlous plight is in no way indicative of the state of the wider field of threatened species managed by DoC.
I have worked for the department for 15 years on threatened-plant con­servation management. Unlike much of its fauna, New Zealand’s flora has never been specifically protected by law. The only attempt to see that it was took place in the 1930s, when a small group of alpine-plant enthu­siasts sought legal protection for native plants. Their lobbying resulted in the Native Plants Protection Act of 1934, a quaint piece of legisla­tion which by today’s standards offers minimal deterrents to plant collection. A promised schedule of “threatened plants” was prepared but never appended. Nevertheless, this act stands as the only enforce­able law protecting the country’s indigenous flora outside the DoC estate. Legend has it that the only time the act was invoked—when the roadside pohutukawa of an irate resident on Auckland’s North Shore was trimmed by the local council—it was ruled that pohutukawa was not a plant but a tree, and the case was thrown out.
New Zealand’s threatened plants continued to receive minimal atten­tion until the mid-1970s, when Dav­id Given, of the Botany Division of the old Department of Scientific and Industrial Research, started a register of threatened natives, and then, in 1981, wrote Rare and Endangered Plants of New Zealand, an excellent popular account of the plight of New Zealand’s flora. Given was also the first to draw up lists (with regular updates from 1976 to 1990) of threatened species rated according to the degree of threat. Initially he used the International Union for the Conservation of Nature (IUCN) Red Data Book categories of “extinct”, “endangered”, “vulnerable” and “rare”. Recognising, however, that New Zealand had many uncom­mon but not necessarily threatened species, Given also introduced the term “local” to cover these. Given’s last sole-author listing in 1990 noted 270 plant species as threatened and a further 99 as local.
Since then the process of listing has been undertaken by the New Zealand Threatened Plant Com­mittee (three lists being published between 1993 and 1999) and its successor, the DoC-sponsored New Zealand Threatened Plant Panel (which has published two lists, in 2002 and 2004).
Though well understood by botanists, listing has been confused by conservation biologists with the internal ranking system used by DoC for prioritising the management of threatened species. DoC’s priority categories have been equated with IUCN threat categories, leading some to claim erroneously that in­creasing numbers of plants are under threat.
In fact, since the introduction of Given’s lists the numbers of seri­ously threatened vascular plants(ferns, conifers and flowering plants) have by and large fallen. Publica­tions within the peer-reviewed literature document a battle being won rather than lost. For example, in 1995 319 vascular plants were considered threatened; by 1999 the figure had fallen to 107. Furthermore, the number of extinct species has remained static at four, with the last presumed extinction—of Adams mistletoe (Trilepidea adamsii)—tak­ing place 50 years ago.
However, in 2002, following the implementation of DoC’s new system for classifying threatened and uncommon species, the number of threatened species rose by 111. Sev­eral factors contributed to this jump.Firstly, the classification system used by the New Zealand Threat­ened Plant Committee had been de­vised for plants only, while the new system was designed for all organ­isms. Adjustments to accommodate animals with small populations were needed. A small population can be an indication of an animal’s immi­nent extinction, but for New Zealand plants small populations are often normal. Such plants, therefore, though listed as “threatened”, were also marked “ST” (stable) or “RC” (recovering) to indicate that they were not actually at risk of extinc­tion.
Secondly, this was only the second time that the entire vascu­lar flora of some 2345 named taxa had been assessed for threat status since 1976. Finally, the system used between 1993 and 1999 applied a very conservative definition of “threatened”. Many taxa previously categorised as “declining”, “recover­ing” or “naturally uncommon” were now listed as “chronically threat­ened” and/or “at risk” even though their numbers had not necessarily declined.
The 218 plant taxa now assessed as “threatened” by DoC, only 122 would have been considered acutely threatened by the New Zealand Threatened Plant Committee, and of these, 13 noted as “stable” and/or “recovering” do not require conservation management. Since 1999, therefore, there has been a net gain of two “threatened” taxa—and this despite the fact that 12 newly described taxa have been placed in the threatened-plant category.
These figures, I believe, show that the plight of New Zealand threat­ened plants is not nearly as bad as was implied by the New Zealand Herald and other media. In fact, the number of threatened plants in New Zealand has remained fairly static over the last 10 years (about 5 per cent of the total flora). The question is whether this result stems from conservation effort or other processes. The Herald article has been interpreted by many as proof that DoC is incapable of managing threatened species appropriately. Is this true?
The question is not as easily an­swered as asked, and statistics don’t always show what they appear to. Some of the reductions in numbers of threatened plants that occurred in the 1990s were attributable to reclassifications following field dis­coveries. For example, the endemic Three Kings Islands tree Elingamita johnsonii, rated as “vulnerable” by the IUCN Red Data Book, was de­scribed in 1951 using sparse material from West Island. Recent and more thorough examinations of this most inaccessible islet have shown that Elingamita is common and occurs also on two adjacent rock stacks. Provided these places remain rat free, Elingamita is not threatened, so has received the new conserva­tion assessment “range restricted”. Comprehensive field surveys have reduced the high IUCN threat status of many other plants.
Although field surveys do not actually entail conservation management, if species’ threat levels can be reduced by the simple expedient of ascertaining their precise status in the wild, surely that is a very cost effective means of reducing the number of taxa requiring direct management. Thirty plant taxa were removed from the threatened-spe­cies list in 2004 simply because field surveys had shown them to be more common than previously believed.
New species are another complication. We keep discovering them, and most are rare or threatened: were they otherwise they would have been discovered earlier. For example, the accidental discovery in 1990 by Dr Brian Molloy of a wheat grass growing on limestone at Castle Hill, Canterbury, has resulted in significant new plant discover­ies on other Canterbury limestone outcrops. Specimens of some of these plants are now being held as safeguards by botanic gardens while they are formally described. A recent Landcare Research monograph on New Zealand gentians recognised five new Gentianella from the south­ern Marlborough, Canterbury and northern Otago limestone areas.
Taxonomic changes are a further factor that muddles the numbers. For instance, of 49 taxa discarded from the threatened-plant lists, 14 were removed because new research had shown they were not taxonomi­cally distinct. A further two species were removed because research had shown them to be failed weed introductions from Australia.
Such arguments aside, is their any evidence that DoC can manage threatened plants successfully? Heaps of it. A small cotula daisy, Leptinella filiformis, once believed extinct and then rediscovered in 1999, is now considered extinct in the wild as its only known habitat was completely destroyed by land developers. Luck­ily DoC and Landcare Research staff foresaw the threat and passed specimens on to botanic gardens, nurseries and specialist native-plant growers. As a result the species has been reintroduced to the wild at several sites, and is also for sale in some garden centres. It can even be seen growing wild in several lawns in urban Auckland. A plant saved by botanists!
The Kermadec koromiko (Hebe breviracemosa), long believed extinct, was rediscovered on Raoul Island by a goat hunter in 1983. Cuttings were raised on the island and in New Zealand, but scientists remained perplexed. How had a species last seen in 1908 reappeared in 1983 when it came from a genus that produced seed only viable for a year or two? Secondly, why did the wild plant fail to throw any seedlings, despite the production of viable seed that could be germinated easily in a nursery?
In 1997, members of the DoC weed team stationed on the island discovered 50 more plants when abseiling down cliffs, thus confirm­ing that the species had probably survived undetected for all those years on cliff faces inaccessible to goats. However, seedlings remained elusive until DoC eradicated rats on Raoul in 2002. Since then they have appeared throughout the island. It now seems likely that seedlings or seeds were being browsed by rats. Currently the world population of the Kermadec koromiko stands at 225 individuals (116 wild and 109 planted), and indications are that within the next 10 or so years this species will have recovered sufficiently to be removed from the threatened-plant list.
Holloway’s crystalwort (Atriplex hollowayi), recognised as new to science in December 2000, is New Zealand’s only endemic strand plant. Growing at or near the high-tide mark on Northland’s sandy beaches, the species was reduced to one indi­vidual in the early 1990s. However, its specific germination and habitat requirements were deduced, and now, through dedicated manage­ment, Holloway’s crystalwort has been brought back from the brink of extinction. So far this season (spring 2004), 80 natural seedlings have appeared and more are expected. These will continue to be supple­mented with cultivated plants. Al­ready the species has been returned to three of its former beach habitats, and so successful has management been that there are plans to return it to parts of its former range near Auckland and in the Bay of Plenty. Barring mishap, its status may soon be reduced from “nationally critical” to “nationally endangered”.
The Three Kings kaikomako (Pennantia baylisiana), often touted as “the world’s rarest tree”, has also undergone a management boost. Known from just one natural specimen on Great Island (Manawa Tawhi), it was long believed func­tionally extinct because the sole survivor was a female. Through a combination of horticultural per­severance and scientific research, flowering plants raised from cuttings from the wild tree have produced viable fruit, as have seedlings raised from these. As a result of information obtained from these studies, the wild tree has also been induced to set viable fruit, and early in 2004 some of these germinated on the island. Though clearly a long way from se­curing the species, management has progressed significantly, and now not only is it anticipated that additional wild plants will be produced, but, should either these or the wild tree fail, there is a large mainland seed bank of genetically pure P. baylisiana to draw upon.
A last example is the coastal pep­percress (Lepidium banksii), one of a group of plants that kept scurvy at bay among Cook’s crews. Of all New Zealand plants this is the one with a death wish, being prone to innumerable attacks by bugs and diseases, having suffered frequent mishaps of nature and nowadays found only in a couple of spots on the Nelson coast. Nevertheless, it has been managed very successfully and rescued from the very brink of extinction. A hundred and eighty-eight adult plants are known from several sites, 12 the result of natural recruitment, the rest of deliberate plantings. Without management, this species would have become extinct by the late 1980s.
While it is true that for some species appropriate management solutions have not yet been deter­mined, and that in some instances we might even be losing the battle, it is clear that in plenty of cases we are winning, both as regards particular species, such as the ones described here, and on the broader front of safeguarding ecosystems. New Zealanders need to hear the good stories about conservation along with the bad. Concerning plants, the stories are mostly good.

Writing in the sixth century AD, Gregory, Bishop of Tours, recorded in his Historia Francorum (The His­tory of the Franks) a dramatic story of the weather intervening in the lives of princes.
In AD 536 there were three rulers of Frankish kingdoms: Childebert, the king of Paris; his brother Lothar, the king of Soissons; and the broth­ers’ nephew Theudebert, the king of Metz. Childebert and Theudebert joined forces and set out with a large army to attack Lothar, who retreated to a fortified position on a hilltop. Hearing of the imminent battle, Queen Clotild, mother of Childebert and Lothar, went to the tomb of Saint Martin and prayed through the night for divine intervention to prevent her sons fighting.
The next morning, before battle preparations had been completed, a terrific thunderstorm laid waste to the aggressors’ camp. Tents were blown down, gear was scattered and horses were driven away by hail and lightning. The hailstones were so large and pelted down with such persistence that many sol­diers, including the two kings, were cut by them, driven to the ground and forced to shelter beneath their shields. Meanwhile, Lothar and his army were untouched by the thun­derstorm. Accepting the event as divine chastisement, Childebert and Theudebert did penance to God,begging forgiveness for attacking their own kith and kin, then sued for peace and concord, which Lothar granted. Lothar’s dynasty prospered, leading eventually to the unification of France and the rule of Charle­magne.
In fact, weather had a significant impact worldwide at this time and, according to David Keys in his fascinating book Catastrophe, may well have changed the course of history. Major droughts and famines are mentioned in records of the Roman and Chinese Empires, and palaeocli­matic records provide confirmation.
One Chinese chronicle, BeiShi, records that in the central Chinese province of Xi’an seven or eight out of every ten people died and the survivors had to eat the corpses. Across the Atlantic, in the Americas, palaeoclimatic data attest to a pro­longed and severe drought. Studies of both bristlecone pine and foxtail pine tree rings in California show a sharp reduction in tree growth consistent with an intense multi­decadal drought. Similar findings have come from tree ring studies in Chile and Argentina. Oxygen-isotope analysis of the shells of freshwater snails found in sediment of a lake in the Yucatan reveal the drought to have been the worst in a thousand years. Analysis of a core taken from an alpine glacier in Peru has shown it to have been the most intense and long-lasting drought recorded.
Archaeologists are now linking this drought to the fall of Teotihua­can, one of the great civilizations of the ancient Americas. With an estimated population of possibly 200,000, the city of Teotihuacan would have been the sixth-largest metropolis in the world at the time. It dominated sixth-century Mexico and Guatemala and traded as far away as present-day New Mexico. Teotihuacan’s largest building, known as the Pyramid of the Sun but probably dedicated to the rain god Tlaloc, was almost as large as the pyramid of Cheops, in Egypt.
Revised dating of the fall of the city now places it several decades after the start of the drought. A study of more than 150 skeletons from a working-class cemetery on the edge of the city shows evidence of a de­cline in health as a drought-induced famine took hold. The death rate for under-25s seems to have doubled, with almost 70 per cent of the work­ing-class population dying before that age. Moreover, the death rate for the age group 15–24 trebled from 8.3 to 27 per cent of all deaths.
Archaeological excavations have shown that the end came violently for Teotihuacan. Most of the pal­aces and temples were burnt to the ground, although the large majority of the residential buildings were not. Religious statues were thrown down from the pyramids and smashed to pieces. One 60-cm-high statue of a goddess has been reassembled from pieces scattered over an area of 860 sq m. Dismembered skeletons surrounded by broken jade and shell jewellery found in the ruins of one of the palaces have been interpreted as the slaughtered remains of priests or rulers. All this is evidence of internal insurrection and the collapse of the state religion based around a rain god who had failed to end the drought.
Great changes were occurring on the other side of the world also. In about AD 550, the Avars, who had ruled the Mongolian steppes since defeating the Huns about 400 years earlier, were overthrown by their vassals, the Turks. David Keys blames the same drought for the Avars’ defeat. Living on grasslands, the Avars had an economy based around the horse, from which they got meat, milk, yoghurt and alcohol (by fermenting mares’ milk), as well as military power. By contrast, the Turks had a more mixed economy, built around cattle, goats, sheep, horses, hunter-gathering activities in the forests and some mining. Horses have a digestive system that is much less efficient than that of cattle. They digest around 25 per cent of the pro­tein they consume, whereas cattle digest around 75 per cent. Hence, the drought hit the horses, and therefore the Avars, much harder than it did the Turks and their cattle. Consequently, the loss of life among the Avars was much greater and the balance of power shifted.
After their defeat, the Avar survi­vors migrated westward, conquer­ing and subjugating the peoples in their path, including the Slavs, before invading the Eastern Roman Empire. The Avars and Slavs enjoyed great success fighting the Romans, winning many battles and carving off large territories over which the Romans never regained control. One of the main reasons the Romans fared so badly was that in the wake of the drought the empire had been ravaged by plague. The population of Constantinople was reduced from about half a million to around 100,000, and other cities were hit as hard. The armies the Romans put in the field were shadows of what they had managed in the past, and the tax base that paid for them had also been decimated.
The arrival of the plague soon after the drought may not have been a coincidence. David Keys argues convincingly that its spread out of central Africa, where it was en­demic, was actually caused by the drought, in the following sequence of events. First the drought caused vegetation to die back, thus reduc­ing the food supply of the rodents that carried the plague. Next, the rodent population fell sharply, as did the populations of rodent predators. When the rains finally returned, the rodents bred much faster than their predators. Then the rodents ex­hausted their local food supply and migrated into surrounding territory, taking the plague with them. Once the plague reached the coast it was carried north to Alexandria along the trade routes by boats carrying ivory for the Roman Empire. From there it raced across Europe and Asia, car­rying away far more lives than the drought itself had.
What caused the drought in the first place? David Keys has an answer for that too—an enormous volcanic eruption near the site of the famous 1883 Krakatoa eruption, in Indonesia. Evidence of a major event in the sixth century has been found in ice cores taken from both the Greenland and Antarctic ice caps. Chinese chronicles record the sound of a loud explosion coming from the direction of Indonesia, while a local chronicle relates the story of an enormous eruption splitting apart the islands of Java and Sumatra.
When a major eruption is directed upwards (as opposed to sideways, which was the case with Mt St Helens in 1980), it can lift enough material into the stratosphere to affect global climate. Although much of the ash and dust falls to earth within months, sulphate aerosols can stay in the stratosphere for years. If the eruption occurs between latitudes 20°N and 20°S, the aerosols can spread over both hemispheres as they migrate slowly polewards. Aerosols block some of the sun’s incoming radiation but do not trap Earth’s outgoing long-wave radiation, resulting in a net cooling of the air. Cooler air is not able to hold as much water vapour as warm air, so cannot produce as much rain. Furthermore, weaker sunlight is less able to initiate showers and thunderstorms by warming the land. Similarly, the various monsoon rains on the different continents would be much reduced by weaker sunlight.
New Zealand has had more than its share of volcanic erup­tions that probably had an impact on the world’s weather in earlier times. Most famously, Taupe's titanic outburst in AD 186 is considered to have been one of the largest erup­tions in the world in the last two or three millennia.
Back in Issue 41 (January–March 1999), we presented preliminary results from the JOIDES Resolution’s deep-sea drilling off New Zealand. Over 600 km east of Gisborne, cores recovered from sediments below the sea floor revealed the presence of 140 layers of volcanic ash which had accumulated over the past 12 million years. The deepest layer was almost a metre deep—a huge amount of ash to be so far east of its eruptive centre, and indicative of a massive event. Indeed, all the ash in these layers was acidic and rhyolitic in nature, characteristics usually associ­ated with huge explosive eruptions. These would have occurred along the Coromandel and Kaimai Ranges and, during the last two million years, in the Rotorua–Taupo zone. Over the last 22,000 years, 80 cubic km of magma has been ejected from the Okataina Volcanic Centre, in the Tarawera area. By comparison, the gentler andesitic eruptions of Ru­apehu and Egmont/Taranaki would have been mere firecrackers.
The June 1991 eruption in the Philippines of Mt Pinatubo—the second-largest eruption of last cen­tury—injected 20 million tonnes of sulphur dioxide into the stratosphere, depressing global temperatures by 0.5° C over the next two years. Al­though eruptions in the tropics more readily affect climates worldwide than do eruptions at higher latitudes, many New Zealand eruptions have been so large that they would have had widespread effects. How we and the world at large might deal with another Taupo is an issue yet to be faced. The climatic consequences of a giant eruption could last for years and affect more people than the eruption itself.

Since 1964 the Marsden Point oil refinery has dominated the southern headland of Whangarei Harbour, giving an industrial stamp to the area. Now, new residential and industrial developments compete for space in the vicinity of the refinery, while across the water the residents of Whangarei Heads watch as their own property values go through the roof. The two harbour heads—each with its distinct character—have become some of the hottest real estate in the north.

Riding massive waves of air that form on the lee side of mountain ranges, modern glider pilots may venture higher into the sky than passengers aboard a jumbo jet. The home of South Island gliding, and host to the Perlan Project—an attempt led by American Steve Fossett to soar to 100,000 ft (30,500 m)—is the airfield at Omarama, North Otago. Marty Taylor, here performing a loop above the Benmore Range at a modest 2000 ft (610 m), headed there to reach for the blue yonder.

It is 100 years since the tiny seeds of a plant known as the monkey peach in its native China were first sown in New Zealand. After making only modest headway in its first half-century of cultivation under the name of Chinese gooseberry, the distinctive green fruit with the stubbly brown skin has since taken off around the world. Rechristened the kiwifruit, it is now the country’s main horticultural export and looks set to become a family of fruits—some of its members very richly coloured, if these slices from experimental crossbred fruit are anything to go by.